Transducers that translate forces, pressures, displacements, etc. into electrical signals that can be used to measure such forces, pressures, displacements, etc. are used in many applications. A currently popular type of such transducer is a Kulite Type BG-10, manufactured by Kulite Semiconductor Products, Inc. Although these semiconductor strain gauge transducers are widely used, they can suffer from a number of drawbacks, such as being easily damaged by slight overloads applied to the force beam, causing the transducer to be non-functional, or have a very large offset voltage, that may not be able to be compensated for in electronic amplifiers.
As mentioned in the above paragraph the semiconductor style of strain gauge is very fragile when made for a low force/weight application, where the gauge itself is physically small. The semiconductor gauges are glued onto the force beam in an area that has a milled-out pocket in the metal beam. This gives an area that “moves” in relation to the applied forces. If the force beam is moved sharply or has more force applied to it than recommended, which can easily happen by dropping the gauge, or over tightening a screw to attach a load to the force beam, the glue holding the gauges may let go, or one or more of the glass-like semiconductor gauges may break making a very expensive device inoperative. If the semiconductor gauge is subjected to larger-than-recommended forces, a large offset voltage may appear on the output signal. This offset voltage may be 2-3 times greater than the desired force signal and may be large enough to not allow compensation by offset controls in signal conditioning equipment.
Another type of transducer available is a capacitive force transducer typically used for measuring small biological force signals. These devices typically contain a free-running resistor-capacitor (RC) oscillating circuit, which generally has a practical upper frequency limit of about 3 MHz due to instability issues. While free-running RC oscillating circuits can go into the hundreds-of-MHz range, stability becomes a major problem at such high frequencies. Even at 1 MHz, the task of frequency compensation is tedious because of the need to hand-select compensation components and oven-test the devices. In addition, the low operating frequency of such a free-running circuit requires the capacitor to be physically large. This slows the response of the circuit to fast external signals and limits the upper frequency range because a small external force must overcome the “at-rest” position of the capacitor plates. A particular 1-MHz free-running RC-circuit-type capacitive transducer investigated by the present inventor was about 2 inches square and about 0.75 inch thick. This large size limits the usefulness of the transducer.